The present invention relates to earthworking implements such as backhoes of the type disclosed in Long U.S. Pat. No. 3,047,171.
For many years now it has been common to mount the backhoe support structure or swing tower on a frame and utilize a pair of hydraulic fluid rams for pivoting the tower with respect to the frame. In such a unit, the hydraulic cylinders are usually connected to the boom support or swing tower on opposite sides of the vertical pivot axis between the swing tower and the frame.
For example, in the above mentioned Long patent, the free ends of the piston rods of the fluid rams are connected to the frame structure at spaced locations while the cylinders of the fluid rams are connected at transversely spaced points to the swing tower or mast.
In recent years, an earthworking implement of the type disclosed in the Long patent has also been mounted in a manner that the entire unit can be shifted transversely with respect to the vehicle. An example of such unit is shown in U.S. Pat. No. 3,436,099 In this patent, the frame supporting the mast or tower is supported on transversely extending rails that are secured to the rear end of the vehicle. This allows the operator to position the frame in any one of an infinite number of positions with respect to the fixed rails and readily lock the unit with respect to the rails.
One of the problems encountered with a transversely shiftable unit of the type discussed above, is the limit of transverse shifting of the earthworking implement with respect to the vehicle. The length of the transversely extending rail is of necessity limited to the width of the vehicle so that the opposite ends of the rails do not extend beyond the outer edges of the rear wheels. Thus, in order to allow for sufficient transverse shifting of the earthworking unit, it has been proposed to mount all of the frame structure as well as the fluid rams rearwardly of the wheels of the vehicle to allow sufficient space so that the unit can be shifted transversely the desired amount. Such a proposed unit thus is capable of being shifted transversely a sufficient distance so that an operator can move the backhoe unit in alignment with the rear wheels and the implement can be used to dig directly adjacent a wall. However, such a unit has the disadvantage of having the center of gravity of the unit located substantially rearwardly of the rear axle for the vehicle. This presents substantial problems, particularly when the unit is being transported since the vehicle experiences a great deal of bouncing because of the substantial moment arm for the implement with respect to the rear axle of the vehicle.
Another proposal for mounting a backhoe on a vehicle so that a trench can be dug parallel to an obstruction, such as a building, is proposed in U.S. Pat. No. 3,250,410. This patent incorporates a complicated supporting structure for the frame that supports the backhoe and only one of the two fluid rams is utilized for swinging the unit in a given direction.